Method of arthroplastly on a knee joint and apparatus for use in same

ABSTRACT

A method of, and apparatus for, arthroplasty of a knee joint comprising obtaining a desired spacing of the femur from the tibia by inserting a spacer into the knee joint between the femur and the tibia. The spacer is used as a reference for securing a guide jig in position about the knee joint for guiding resection of one or both of the femur and tibia for fitting of tibial and/or femoral prostheses. A method of resecting the femur while moving the tibia through an arc of motion to remove bone to the desired depth, a method of determining the position of the guide jig, the guide jog, an alignment device and the spacer are also described.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of International ApplicationNo. PCT/AU01/00258 filed on Mar. 9, 2001 and published in English asInternational Publication Number WO 01/66021 A1 on Sep. 13, 2001, whichclaims priority to Australian Patent Application No. PQ 6161 filed onMar. 10, 2000, Australian Patent Application No. PQ 8999 filed on Jul.25, 2000, Australian Patent Application No. PQ 9044 filed on Jul. 27,2000, and Australian Patent Application No. PQ 9045 filed on Jul. 27,2000.

FIELD OF THE INVENTION

[0002] The present invention relates to a method of arthroplasty on aknee joint of a patient. The method extends to both unicondylar kneearthroplasty and knee joint arthroplasty involving resection of both thelateral and medial condyles of the tibia and femur. There is alsoprovided apparatus for use in the method.

BACKGROUND OF THE INVENTION

[0003] Various methods and apparatus for performing knee arthroplastyand unicondylar knee arthroplasty in particular, are known in the art.The known methods involve resection of the tibia and femur for fittingof trial tibial and femoral implants, respectively. Once the bone hasbeen resected and the trial implants are secured in place, the surgeonthen assesses the kinematics of the knee joint. At this stage, thesurgeon may transect, elevate and/or release ligaments and other softtissue structures to achieve the desired level of deformity correction,balance in the tension of relevant ones of the ligaments and otherstabilising soft tissue structures, and an acceptable range of motion ofthe knee joint. Additional bone resection may also be required toachieve the desired outcome. This leads to an increase in operation timewith an associated increase in the risk of surgery relatedcomplications. Moreover, such additional surgical intervention followingfitting of the trial implants potentially leads to subsequent increaseddiscomfort for the patient and increased healing times. Methods andapparatus for use in arthroplasty of a knee joint are exemplified inU.S. Pat. No. 5,171,244 and U.S. Pat. No. 5,520,695.

SUMMARY OF THE INVENTION

[0004] It is an aim of the present invention to ameliorate one or moreproblems of the prior art or at least provide an alternative to theprior art.

[0005] In one aspect of the invention there is provided a method ofarthroplasty on a knee joint, comprising the steps of:

[0006] (a) obtaining a desired spacing of the femur from the tibia;

[0007] (b) determining depth of bone to be resected from at least one ofthe tibia and the femur on the basis of the desired spacing of the femurfrom the tibia to enable fitting of at least one prosthesis selectedfrom tibial and femoral prostheses;

[0008] (c) resecting bone from one or both of the tibia and the femursubstantially to the determined depth in the or each one, respectively;and

[0009] (d) fitting the or each said prosthesis.

[0010] The method is particularly suitable for use in unicondylar kneearthroplasty but may also be used in bicondylar knee arthroplastyinvolving resection of the lateral and medial condyles of both the tibiaand the femur. By unicondylar knee arthroplasty is meant arthroplastyinvolving resection of either the lateral or medial condyles of thetibia and the femur.

[0011] The resection of the bone may comprise cutting at least one ofthe tibia and the femur substantially at the appropriate determineddepth in the or each one of the tibia and the femur to remove a segmentof bone from the or each one.

[0012] Preferably, the resection of the bone from the tibia may compriseforming a recess in the uppermost end of the tibia adjacent to the femurfor receiving the tibial prosthesis.

[0013] Accordingly, in another aspect of the present invention there isprovided a method of arthroplasty on a knee joint, comprising the stepsof:

[0014] (a) surgically providing access to the knee joint;

[0015] (b) obtaining a desired spacing of the femur from the tibia;

[0016] (c) determining depth of bone to be resected from an end of thetibia to form a recess for receiving a tibial prosthesis on the basis ofthe desired spacing of the femur from the tibia;

[0017] (d) resecting the bone from the tibia to the determined depth toform the recess; and

[0018] (e) positioning the tibial prosthesis in the recess.

[0019] The method may further comprise locating a guide jig in positionabout the knee joint for guiding the resection of the bone. Preferably,the guide jig will be adapted for guiding movement of a cutter devicerelative to the tibia for shaping the recess to a desired profile. Mostpreferably, the jig will incorporate a template for guiding the movementof the cutter device relative to the tibia.

[0020] Preferably, bone will be resected from both the tibia and thefemur to enable the fitting of both the tibial and the femoralprostheses.

[0021] Preferably, the desired spacing of the femur from the tibia willbe obtained using at least one spacer inserted into the knee jointbetween the femur and the tibia to thereby provide the spacing.

[0022] In unicondylar knee arthroplasty only a single spacer willusually be used to obtain the desired spacing of the femur from thetibia. In contrast, in bicondylar knee arthroplasty a pair of spacerswill usually be utilised, one being located between each of the lateraland medial condyles of the femur and the tibia, respectively. In thisinstance, the spacers may have the same thickness or a differentthickness to each other.

[0023] Most preferably, the or each spacer will be adapted for beingpositioned between corresponding ones of the condyles of the femur andthe tibia.

[0024] In another aspect of the present invention there is provided amethod of arthroplasty on a knee joint, comprising the steps of:

[0025] (a) surgically providing access to the knee joint;

[0026] (b) selecting at least one spacer for providing desired spacingof the femur from the tibia;

[0027] (c) positioning the selected spacer in the knee joint to obtainthe desired spacing of the femur from the tibia;

[0028] (d) using the spacer as a reference to determine a location oneach one of the tibia and the femur indicating depth of bone to beresected from each for fitting of chosen tibial and femoral prostheses;

[0029] (e) cutting the tibia and the femur substantially at thedetermined location on each for resection of the bone from each one tothe required said depth; and

[0030] (f) fitting the chosen tibial and the femoral prostheses.

[0031] Typically, the knee joint will be placed in a position of flexionwhereby the tibia is arranged at an angle with respect to the femur forthe resection of the bone. Generally, bone will be resected from aposterior side of the femur and the uppermost end of the tibia.

[0032] Preferably, a method of the invention will comprise selecting theat least one spacer from a range of spacers for providing differentspacings of the femur from the tibia. Accordingly, the selecting of theor each spacer may comprise;

[0033] (i) choosing the spacer from a range of spacers for providing adifferent spacing of the femur from the tibia, respectively; and

[0034] (ii) moving the tibia about the femur through an arc of motionbetween backward and forward positions to evaluate movement of the kneejoint while the chosen spacer is in position in the knee joint betweenthe femur and the tibia.

[0035] The selecting may further comprise repeating steps (i) and (ii)as necessary to obtain the desired spacing of the femur from the tibiausing a different spacer chosen from the range of spacers each time.

[0036] The selected spacer will usually be of a thickness for providingappropriate tension and optimising balance in the action of variousligaments and other soft tissue structures of the knee joint during themovement of the tibia about the femur. Preferably, the tension in theknee joint obtained by the spacing of the femur from the tibia with theuse of the selected spacer will be substantially retained upon thefitting of the or each prosthesis.

[0037] Preferably, the guide jig will be adapted for guiding resectionof bone from each of the tibia and the femur. The securing of the guidejig may comprise arranging the jig with the spacer to facilitate thepositioning of the jig about the knee joint.

[0038] Knowing the relevant dimensions of the chosen tibial and femoralprostheses allows the guide jig to be adapted such that when arrangedwith the spacer, the guide jig is positioned relative to the tibia andthe femur for guiding the cutting of the one or both of them at thedepth in the resection of bone therefrom for accommodating the tibialand femoral prostheses. Accordingly, the selected spacer has two rolesin unicondylar knee arthroplasty, firstly to space the femur from thetibia and secondly, to act as a reference for resection of bone from oneor both of the tibia and the femur to the correct depth.

[0039] Therefore, in a further aspect of the invention there is provideda method of determining the position of a guide jig about a knee jointfor subsequently guiding resection of one or both of the tibia and thefemur to a desired depth in the or each one, respectively, the methodcomprising:

[0040] (a) locating a selected spacer in the knee joint to obtain adesired spacing of the femur from the tibia; and

[0041] (b) arranging the guide jig and the spacer together to therebydetermine the position of the guide jig for guiding the resection of theone or both of the tibia and the femur.

[0042] In addition, a combination approach for resecting bone from thefemur to the desired depth may be employed. This may involve resecting asegment of bone from the femur to the desired depth in that boneutilising a guide jig as herein described, and inserting an appropriatecutter device into the knee joint between the tibia and the femur in theabsence of the guide jig, for resecting bone from the femur withoperation of the device and upon movement of the tibia in an arc ofmotion about the femur to thereby resect further bone from the femur tothe desired depth in that bone for fitting of a femoral prosthesis. Ifdesired, only the latter one of those steps may be employed in theresection of the bone from the femur.

[0043] Accordingly, in another aspect of the present invention there isprovided a method of arthroplasty on a knee joint, comprising the stepsof locating a cutter device in position in the knee joint between thetibia and the femur, and moving the tibia through an arc of motion aboutthe femur between backward and forward positions while the cuttingdevice is being operated and is in position between the tibia and thefemur, to thereby remove bone substantially to a desired depth from thefemur in a direction of travel of the tibia relative to the femur.

[0044] There is also provided apparatus for use in the methods of theinvention.—Apparatus as described herein may be provided in kit form oras an assembled arrangement.

[0045] Hence, in a still further aspect of the present invention thereis provided apparatus for use in a method of arthroplasty on a kneejoint of a patient, comprising:

[0046] a guide jig for guiding cutting of at least one of the tibia andthe femur in resection of bone therefrom for enabling fitting of one orboth of a tibial and a femoral prosthesis, wherein the guide jig isadapted for being arranged with at least one selected spacer for spacingthe femur from the tibia, and for being secured about the knee joint ina position determined by the spacer to guide cutting of the at least oneof the tibia and the femur substantially at a desired depth in the oreach one, respectively.

[0047] Typically, the guide jig will be adapted for guiding cutting ofthe tibia at a fixed predetermined distance below the spacer.Preferably, the guide jig will be adapted for guiding cutting of boththe tibia and the femur when the guide jig is secured about the kneejoint in said position.

[0048] Accordingly, in yet another aspect of the invention there isprovided apparatus for use in a method of arthroplasty on a knee jointof a patient, comprising:

[0049] a guide jig for guiding cutting of the tibia and the femur inresection of bone therefrom for enabling fitting of chosen tibial andfemoral prostheses, and being adapted for being secured about the kneejoint in a position determined by at least one spacer for providing adesired spacing of the femur from the tibia, to guide the cutting of thetibia and the femur at a desired depth in each one, respectively.

[0050] In still another aspect of the invention there is providedapparatus for use in a method of arthroplasty on a knee joint of apatient, comprising:

[0051] (a) at least one spacer having a predetermined thickness forproviding a desired spacing of the femur from the tibia; and

[0052] (b) at least one guide jig for guiding cutting of the tibia andthe femur for resection of bone to a desired depth from the or each onerespectively, to enable fitting of chosen tibial and femoral prostheses;

[0053] wherein the guide jig is adapted for being secured about the kneejoint in a position determined by the spacer to guide the cutting of theor each one of tibia and the femur substantially at the desired depth inthe or each one.

[0054] The spacer will normally be provided as one of a set of spacersfor providing different spacings of the femur from the tibiarespectively, thereby allowing the selection of different ones of thespacers as needed.

[0055] Hence, in yet another aspect of the present invention there isprovided apparatus for use in a method of arthroplasty on a knee jointof a patient, comprising;

[0056] (a) a set of spacers for allowing selection of at least one saidspacer for insertion into the knee joint for providing a desired spacingof the femur from the tibia; and

[0057] (b) at least one guide jig for guiding cutting of one or both ofthe tibia and the femur for resection of bone to a desired depth fromthe or each one respectively, to enable fitting of chosen tibial andfemoral prostheses;

[0058] wherein the guide jig is adapted for being secured about the kneejoint in a position determined by the spacer to guide the cutting of theone or both of tibia and the femur substantially at the desired saiddepth in the or each one, and wherein the spacers have a differentthickness to one another for providing different spacings of the femurfrom the tibia.

[0059] The guide jig may be adapted for guiding the cutting of the femurand the tibia at the same depth in each one or at a different depth inthe tibia compared to the femur.

[0060] Preferably, the guide jig will be adapted for guiding the cuttingof the tibia and the femur at a predetermined fixed spacing. The guidejig will normally be adapted for being coupled with one or more saidspacers. The term“coupled” is to be taken in the broadest sense andincludes within its scope reception of the spacer(s) by the jig whetherthe or each spacer is fixed to the guide jig or not.

[0061] Preferably, the guide jig will comprise a cutting block adaptedfor receiving the or each selected spacer and most preferably, will havea through passageway for guiding the cutting of one of the condyles oftibia and the femur. More preferably, the guide jig will have anotherthrough passageway for guiding the cutting of the other of the condyles.Most preferably, the cutting block will be adapted for being secured tothe tibia.

[0062] Generally, the guide jig will be adapted for guiding cutting ofone or both of the tibia and the femur in a medial to lateral or lateralto medial direction with respect to the knee joint.

[0063] Preferably, the guide jig will be adapted for being secured aboutthe knee joint in a position determined by the thickness of the spaceror spacers used.

[0064] In another aspect of the present invention there is provided aspacer for being inserted into a knee joint for spacing the femur fromthe tibia, comprising an elongate member with a leading end regionadapted for being positioned between the tibia and the femur to spacethe femur from the tibia, and an opposite end region for protruding fromthe knee joint.

[0065] In a further aspect of the present invention there is provided aspacer for being inserted into a knee joint to provide a desired spacingof the femur from the tibia in arthroplasty on the knee joint,comprising an elongate member with a leading end region adapted forbeing inserted between the tibia and the femur to thereby obtain thedesired spacing of the femur from the tibia and being retained in theknee joint during resection of bone to a desired depth from one or bothof the tibia and the femur respectively, and an opposite end regionadapted for protruding from the knee joint and coupling with a guide jigfor guiding the cutting of the or each one of the tibia and the femur inthe resection of the bone.

[0066] Preferably, the leading end region of the spacer will be adaptedfor retaining the spacer in the knee joint. Most preferably, the leadingend region of the spacer will be adapted for receiving the medial orlateral condyle of the femur for retaining the spacer in the knee joint.

[0067] In yet another aspect of the present invention there is provideda set of spacers for allowing selection of at least one of the spacersfor insertion into a knee joint to provide a desired spacing of thefemur from the tibia in arthroplasty on the knee joint, each said spacerrespectively comprising an elongate member with a leading end regionadapted for being inserted between the tibia and the femur to therebyspace the femur from the tibia and being retained in the knee jointduring resection of bone from one or both of the tibia and the femurrespectively, and an opposite end region adapted for protruding from theknee joint and coupling with a guide jig for guiding cutting of the oreach one of the tibia and the femur in the resection of the bone,wherein the spacers have a different thickness to one another forproviding different spacings of the femur from the tibia.

[0068] Usually, it is desirably to resect the tibia at an angle slopingdownwardly in the anterior to posterior direction of the knee joint forlocation of the tibial prosthesis on the resulting sloping surface ofthe tibia. Typically, the angle of slope is about 3° although this mayvary from patient to patient.

[0069] Accordingly, in another aspect of the present invention there isprovided an alignment device for aligning a guide jig in position abouta knee joint for guiding cutting of at least one of the tibia and thefemur at a desired location on the or each one respectively duringarthroplasty on the knee joint, and comprising:

[0070] a body for receiving the guide jig and coupling the guide jigwith an alignment guide for aligning the guide jig in a desired medialto lateral orientation with respect to the knee joint;

[0071] and wherein the body is adapted for aligning the guide jig at adesired angle in an anterior to posterior direction of the knee jointfor securing of the guide jig at the desired angle prior to removal ofthe body from about the knee joint for allowing cutting of the one orboth of tibia and the femur to be guided by the guide jig.

[0072] In still another aspect of the present invention there isprovided an alignment device for supporting a cutting device forresecting bone from the tibia to a desired depth to from a recess in thetibia during arthroplasty on a knee joint, and comprising:

[0073] a body for receiving a guide jig for guiding cutting of the femurand coupling the guide jig with an alignment guide for aligning theguide jig in a desired medial to lateral orientation with respect to theknee joint;

[0074] and wherein the body is adapted for aligning the guide jig at adesired angle in an anterior to posterior direction of the knee jointand for being secured about the knee joint in a position determined bythe guide jig for supporting the cutting device for the resection of thebone from the tibia following removal of the guide jig from the body.

[0075] Accordingly, there is also provided an alignment guide forsupporting the guide jig and aligning the guide jig in a desired medialto lateral orientation with respect to the knee joint to allow for varusand valgus adjustment.

[0076] The alignment guide will typically incorporate a mountingplatform which is angularly displaceable for allowing orientation of theguide jig in the medial to lateral direction. Desirably, the mountingplatform will be adapted for supporting the guide jig adjacent to themedial condyles of the tibia and femur or the lateral condyles of thebones as may be required. The alignment guide will generally be a tibialalignment guide for being secured along the leg of the patient inalignment with the tibia.

[0077] Alternatively, the guide jig itself may be adapted for guidingthe cutting of one or both of the tibia and the femur at the desiredangle in the medial to lateral direction of the knee joint. Similarly,the guide jig may be adapted for guiding cutting of the one or both ofthe tibia and femur at the downward angle in the anterior to posteriordirection of the knee joint, in which case the alignment componentdescribed above for this purpose may not be utilised and the cuttingblock may be mounted directly on the alignment guide.

[0078] In still another aspect there is provided the use of a guide jigof the invention in the assembly of a medical device for arthroplasty ofthe knee, wherein the medical device comprises the guide jig and atleast one spacer for spacing the femur from the tibia.

[0079] In still another aspect there is provided the use of at least onespacer of the invention in the assembly of a medical device for guidingresection of bone from at least one of the tibia and the femur inarthroplasty of the knee.

[0080] In a further aspect there is provided the use of at least onespacer of the invention in the assembly of a medical device for kneearthroplasty, wherein the medical device comprises the or each spacerand a guide jig of the present invention.

[0081] Advantageously, the method of the invention may allow balancingof tension in ligaments and other soft tissue structures of the kneejoint to be optimised prior to resection of bone for the fitting of theprostheses. Moreover, ligament and soft tissue release to obtainadequate balancing of tension in the ligaments and soft tissue of theknee joint during flexion and extension of the knee joint as is requiredfor optimum knee joint kinematics prior to or following fitting of trialtibial and femoral implants may be eliminated or reduced.

[0082] In addition, the risk of incorrect alignment and orientation ofthe tibial and femoral prostheses relative to one another with referenceto the action of the ligaments and soft tissue structures may bereduced.

[0083] It is another advantage that as the use of a spacer or spacers asherein described may facilitate both positioning of the guide jig andappropriate tensioning of ligaments and other soft tissue structures ofthe knee joint, decreased operating times may be provided therebypotentially reducing the incidence of various time related surgicalcomplications such as wound infection, complications associated with therisk of anaesthetic, and thrombosis associated with tourniquetapplication which can lead to pulmonary embolus and other seriousproblems. Furthermore, by reducing the need to transect, elevate, orrelease ligaments and other soft tissue structures of the knee joint,post-operative recovery time may be reduced with consequentialreductions in overall health care costs associated with kneearthroplasty.

[0084] Unless the context clearly requires otherwise, throughout thedescription and the claims, the words ‘comprise’, ‘comprising’, and thelike are to be construed in an inclusive sense as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to”.

[0085] The features and advantages of the present invention will becomefurther apparent from the following detailed description of a number ofpreferred embodiments illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0086]FIG. 1 is a side schematic view illustrating a knee joint withtibial and femoral prostheses fitted;

[0087]FIG. 2 is an anterior view of the fitted tibial and femoralprostheses shown in FIG. 1;

[0088]FIG. 3 is a perspective view of the femoral prostheses shown inFIG. 1 prior to being fitted;

[0089]FIG. 4 is a perspective view of the tibial prostheses shown inFIG. 1 prior to being fitted;

[0090]FIG. 5 is a diagrammatic front view of a knee joint;

[0091]FIG. 6 is a diagrammatic front view showing a spacer in positionbetween a femur and a tibia of the knee joint illustrated in FIG. 5;

[0092]FIG. 7 is a diagrammatic side view of a set of different spacers,for providing different spacing of the femur from the tibia;

[0093]FIG. 8 is a perspective exploded view of apparatus for performingarthroplasty on a knee joint;

[0094]FIG. 9(a) is a perspective view of the apparatus of FIG. 8 whenassembled;

[0095]FIG. 9(b) is a diagrammatic front view of the apparatus of FIG. 8fitted to the leg of a patient;

[0096]FIG. 10(a) is a rear perspective view of a guide jig of theapparatus shown in FIG. 8;

[0097]FIG. 10(b) is a side view of the guide jig of FIG. 10(a);

[0098]FIG. 11 is a view of an alignment component of the apparatus shownin FIG. 8.

[0099]FIG. 12 is a schematic plan view of the guide jig of FIG. 10indicating the orientation of channels defined in the jig for receptionof pins for securing the jig in position about the knee joint;

[0100]FIG. 13 is a diagrammatic partial view of a tibial shaft;

[0101]FIG. 14 is a diagrammatic front view of the guide jig fitted inposition about the knee joint;

[0102]FIG. 15 is a front diagrammatic view showing the medial condylesof the femur and the tibia following resection thereof;

[0103]FIG. 16 is a diagrammatic view illustrating the use of a tibialsizing device for determination of an appropriate size of tibialimplant;

[0104]FIG. 17 is a perspective view of a tibial trial;

[0105]FIG. 18 is a diagrammatic view of the tibial trial of FIG. 17;

[0106]FIG. 19 is a diagrammatic anterior view of the tibial implant ofFIG. 16 fixed in position on the tibia of the knee joint;

[0107]FIGS. 20 and 21 are diagrammatic views illustrating marking of afemoral condyle of the knee joint for further resection of the femur toenable fitting of the femoral prosthesis of FIG. 3;

[0108]FIG. 22 is a diagrammatic view illustrating the use of a femoralsizer for determination of the appropriate sized femoral prosthesis;

[0109]FIG. 23 is a diagrammatic view illustrating the use of a femoralshaping rasp for shaving bone from the relevant condyle of the femur toenable fitting of the femoral prosthesis;

[0110]FIG. 24 is a diagrammatic view illustrating the use of a femoralpeg drill guide to drill a bore into the femur for reception of thefemoral peg of the femoral prosthesis shown in FIG. 3;

[0111]FIG. 25 is a perspective view of a tibial implant of theinvention;

[0112]FIG. 26 is a diagrammatic view of the tibial implant of FIG. 25fixed in position on the tibia;

[0113]FIG. 27(a) is an elevated side view of a cutting device forresecting bone from the femur;

[0114]FIG. 27(b) is a perspective view of the cutter blade disk of thecutting device of FIG. 27(a);

[0115]FIG. 28 is an end view of the cutting device of FIG. 27(a);

[0116]FIG. 29 is a side view of the cutting device of FIG. 27(a);

[0117]FIG. 30(a) is a longitudinal cross-sectional view of the cuttingdevice of FIG. 27(a);

[0118]FIG. 30(b) is a diagrammatic partial view of a couplingarrangement used for coupling the head and body of the cutter device ofFIG. 27(a) together;

[0119]FIGS. 31 and 32 illustrate reception of the cutting device of FIG.27(a) the tibial implant of FIG. 25 in unicondylar arthroplasty;

[0120] FIGS. 33(a) to 33(c) illustrate the resection of bone to adesired depth from the femur;

[0121]FIG. 34 is an exploded perspective view of an assembly for forminga recess in the tibia for receiving a tibial implant;

[0122]FIG. 35 is an exploded perspective view of the apparatus of FIG. 8when arranged for removal of bone from the tibia for inset placement ofa tibial implant;

[0123]FIG. 36 is a perspective view of the apparatus arranged as shownin FIG. 35 when assembled;

[0124]FIG. 37 illustrates removal of bone from the tibia for insettibial implant placement utilising apparatus of the invention; and

[0125]FIG. 38 illustrates a further cutting device for resecting bone toa desired depth from the femur.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE PRESENT INVENTION

[0126] The femoral prosthesis 2 shown in FIG. 1 is fitted to the medialcondyle 4 of the femur 6 and abuts articulating surface 8 of the tibialprosthesis 10 fitted on the corresponding medial condyle 12 of the tibia14, for articulation thereon as the tibia undergoes flexion andextension about the knee joint 15. The positioning of the femoralprosthesis 2 and the tibial prosthesis 10 is more clearly shown in FIG.2.

[0127] As shown in FIG. 3, the femoral prosthesis 2 is provided with acentrally orientated upstanding fin 16 incorporating a peg 18 projectingfrom an interior face 20 of the prosthesis.

[0128] The opposite outer face 22 has a curved contour for facilitatingmovement of the tibia about the femur. The interior face 20 of thefemoral prosthesis is textured to enhance binding of bonding cement usedto fix the prosthesis to the femur. The prosthesis itself is formed froma cast cobalt chromium molybdenum alloy conventionally used in themanufacture of such prostheses.

[0129] The tibial prosthesis 10 shown more clearly in FIG. 4 ismanufactured from ultra high molecular weight polyethylene and has adove tailed base 24 to again enhance bonding of cement to the prosthesisfor fixing the prosthesis to the tibia. The articulating surface 8 ofthe tibial prosthesis is sightly concaved to substantially matchcurvature of the outer face 22 of the femoral prosthesis.

[0130] An example of unicondylar arthroplasty will now be described. Asa first step, a longitudinal incision is made in the knee from justmedial to the medial edge of the patella 26 to just below the medialtibial plateau adjacent to the attachment of the iliotibial tract, asindicated by the dotted line in FIG. 5. The incision avoids transectingany of the ligamentous structures that contribute to the kinematics ofthe knee. The patella is not everted, but gently retracted laterally toexpose the medial compartment of the knee. All femoral and tibialosteophytes which are accessible are then removed.

[0131] In order to balance tension in ligaments and other soft tissuestructures of the knee joint as well as to correct deformity, a spacer28 is located in position between the condyle of the femur and thecorresponding condyle of the tibia as shown in FIG. 6. The spacereffectively spaces the femur from the tibia.

[0132] To check for adequate tension of the soft tissue structures andkinematics of the knee joint, the tibia is moved through an arc offlexion of between 0° to about 130°. If the knee joint is unstable orhas inadequate tension, the spacer may be removed and a spacer having agreater thickness for spacing the tibia and the femur further apart maybe located in the joint. Conversely, if the knee feels over tensioned oradequate range of movement through the arc of flexion cannot beachieved, the spacer may be replaced with a spacer having a reducedthickness to decrease the spacing between the femur and the tibia. Thisprocess may be repeated a number of times using a spacer having adifferent thickness each time until adequate tension and kinematics ofthe knee joint is achieved.

[0133] Importantly, the method enables the tensioning of soft tissuestructures in the knee joint to be optimised prior to any bone beingresected from the tibia or the femur in preparation for fitting of thetibial and femoral prostheses. Moreover, the tensioning may be obtainedwithout the need to transect, elevate or release soft tissue structuresof the knee joint. However, further adjustment of the tensioning in theknee joint as may be deemed necessary using such procedures is notexcluded.

[0134] A set of spacers from which the appropriate spacer 28 may beselected is illustrated in FIG. 7. The spacers each comprise an elongatebody 30 for being inserted into the knee joint between opposing condylesof the tibia and the femur. The body 30 has a bulbous protrusion 32formed on an underside of a leading end region 34 thereof for beingseated on the sulcus of the relevant tibial condyle. As can be seen, theleading end region of each spacer is scooped upwardly forward oftransverse ridge 35 thereby defining a trough 36 for receiving thecondyle of the femur. The scooped contour of the leading end region ofthe spacer facilitates insertion of the spacer into the knee joint andassists in retaining the spacer in position once located in the kneejoint.

[0135] As will be appreciated, the spacing of the femur from the tibiais determined by the thickness of the bulbous protrusion. In the spacerset shown, the thickness of the respective spacers increases in 1 mmincrements. However, sets of spacers having a different thickness rangemay of course be used instead.

[0136] Once the appropriate spacer 28 has been selected and located inposition in the knee joint, apparatus as shown in FIG. 8 for guidingcutting of the tibia and the femur for resection of bone therefrom issecured in position about the knee joint. The apparatus comprises aguide jig in the form of a tibiofemoral cutting block 38 adapted forbeing securely mounted on mounting platform 40 of tibial alignment guide42.

[0137] Tibial alignment guide 42 is adapted for being aligned along thelongitudinal axis of the tibia and the mounting platform 40 is able tobe angularly adjusted relative thereto about pivot 44 to accommodaterequired varus or valgus adjustment in the medial to lateral directionof the knee joint as may be necessary. Angular displacement of themounting platform is achieved by loosening lock nut 52 and rotating theplatform about the pivot pin 44 to the desired angle with reference to ascale (not shown) marked on the front face 54 of the tibial alignmentguide, and subsequently retightening the lock nut 52. Shaft 46 of thealignment guide is telescopic to permit an ankle strap 48 carried on thebracket 50 mounted on the lower end region of the alignment guide to besecured around the ankle.

[0138] A more detailed view of the cutting block 38 is shown in FIG.10(a). As indicated, a number of slots extending through the cuttingblock from a front face 56 to an opposite rear face indicated by thenumeral 58 are defined in the cutting block. In particular, the cuttingblock incorporates an upper slot 60 for guiding cutting of the femur inthe resection of bone therefrom, and a middle slot 62 for receiving theprotruding end region of the spacer when inserted in the knee joint. Alower slot 64 is also defined in the cutting block for reception of reartongue 66 of alignment component 68. The distance between the top 70 ofthe slot 62 and the bottom 72 of the lower slot 64 correspondsessentially to the thickness T of the tibial prosthesis 10 of FIG. 4. Apair of inwardly directed channels 73(a) and 73(b) are also defined inopposite side regions of the cutting block, one in each side regionrespectively, for guiding downwardly directed cuts into the tibia in theresection of bone therefrom. A side view of the cutting block 38 isshown in FIG. 10(b).

[0139] The apparatus when assembled is shown in FIG. 9(a) and whensecured in position about the knee joint in FIG. 9(b). As can be seen,the apparatus further incorporates a stylus 75 for assisting alignmentof the cutting block with the femur and which is mounted on theprotruding end of the spacer 28.

[0140] As shown in FIG. 11, the alignment component consists of a body74 incorporating a forwardly projecting tongue 76 which lies in the sameplane as rearwardly projecting tongue 66 and overlies a long tongue 78of the body provided for insertion into slot 80 or 82 of the mountingplatform 40 of the tibial alignment guide 42. The plane in which theforward and rearward tongues 76 and 66 lie extends at an angle φrelative to the long tongue 78 such that tongue 76 diverges from thelong tongue 78 with distance along the long tongue.

[0141] Accordingly, the cutting block 38 when mounted on the alignmentcomponent and assembled with the tibial alignment guide 42 is orientatedfor guiding resection of bone at a downward angle of φ in the anteriorto posterior direction of the knee joint. Typically, angle φ will be 3°although different alignment components may be provided in which angle φdiffers from one to the next to allow selection of the most appropriateone for each patient. Alternatively, an alignment component may beutilised in which the tongues 66 and 76 lie substantially parallel withthe long tongue 78 in the case where it is desirable for the tibia to becut in a substantially horizontal plane of the tibia.

[0142] As will be appreciated, the slots 80 and 82 of the mountingplatform 40 of the tibial alignment guide are spaced apart from eachother along the mounting platform for allowing the cutting block 38 tobe positioned adjacent to the lateral and medial condyles of either theright or left tibiae, respectively.

[0143] Once the cutting block is secured to the tibia as will bedescribed further below, the alignment component 68 and the tibialalignment guide 42 are removed from about the knee joint withoutdisturbing the cutting block and spacer assembly. This leaves lowerguide slot 72 of the cutting block vacant for reception of a saw andsubsequently guiding cutting of the medial condyle of the tibia in theresection of bone for fitting of the tibial prosthesis. The resection ofbone from the tibia and the femur is performed while the knee is placedin about 90° to about 100° of flexion.

[0144] In this position, the top slot 60 of the cutting block 38 guidesthe saw for cutting of a posterior chamfer from the femoral condyle forfitting of the femoral prosthesis and as such, both the tibia and thefemur are cut in a plane extending in the medial to lateral direction,respectively.

[0145] Channels 84 and 86 are provided in the cutting block forreception of trocar pins 88 for securing the cutting block to the tibia.As shown schematically in FIG. 12, the bottom channels 86 convergetoward each other in the front to the rear direction of the cuttingblock and are obliquely orientated with respect to the top pair ofchannels 84. Apertures 90 defined in the alignment component 68 arepositioned to align with channels 84 of the cutting block when thecutting block is mounted on the tibial alignment guide to thereby holdthe cutting block and alignment component together upon trocar pinsbeing inserted therethrough into the tibia. In this way, the alignmentcomponent can be slid off the free end of the trocar pins leaving thecutting block behind in position about the knee joint.

[0146] In the case of bowed varus tibiae, the cutting block will bearranged substantially perpendicular with respect to the metaphysealaxis of the tibial shaft as indicated in FIG. 13.

[0147]FIG. 14 illustrates the positioning of the cutting block 38 forthe resection of the medial condyles of the tibia and femur while thetibia is placed in flexion with respect to the femur, and with thealignment component 68 and tibial alignment guide 42 removed. Once thetransverse cuts to the tibia and the femur have been performed, adownwardly directed cut into the tibia guided by the relevant one ofchannel 73(a) or 73(b) of the cutting block is performed for removal ofa segment of bone from the tibia to form a recess therein. The cuttingblock 38 and spacer 28 assembly is then removed to allow the downwardlydirected cut into the tibia to be completed. At this time, any remainingposterior osteophytes and meniscus are also removed as required. Theresected medial condyles of the tibia and femur following removal of thecutting block and spacer assembly is shown in FIG. 15. The use of a kneejoint spreader 92 to maintain suitable access to the knee joint space isalso shown. Alternatively, a suitable retractor may be utilised.

[0148] A diagrammatic plan view of the resected tibia is shown in FIG.16. As indicated, following resection of the tibia, a tibial sizingdevice 94 is used to check the anteroposterior dimension of the resectedtibial surface 96 for selection of an appropriately sized tibial trial98 for being pinned into position on the resected surface. An example ofa suitable tibial trial is illustrated in FIG. 17.

[0149] The profile of the tibial trial 98 and its thickness T match thatof the tibial prosthesis 10. As will be appreciated, and with referenceto FIG. 16, the profile of both the tibial trial 98 and tibialprosthesis 10 substantially match the profile of the resected tibialsurface 96 of the tibia.

[0150] A channel in the form of a guide groove 100 is defined across thetibial trial for being orientated in the anteroposterior direction whenthe tibial trial is fitted in position. An obliquely orientated channel102 extends from the side face 104 of the tibial trial through to itsbase 106 for reception of a pin therein for securing the tibial trial tothe tibia. A tab 108 on the posterior side of the tibial trial dependsfrom the base 106 as is more clearly shown in the diagrammatic size viewof the tibial trial shown in FIG. 18, for assisting positioning of thetibial trial on the resected surface of the tibia.

[0151] The tibial trial when secured in position on the resected tibialsurface 96 of the tibia by pin 110 is shown in FIG. 19. To accommodatethe upstanding central fin 16 of the femoral prosthesis 2, areciprocating saw blade is located along the guide groove 100 of thetibial trial and the tibia moved about the femur through an arc ofmotion to cut a channel into the femur indicated by dotted line 112. Inthis way, the groove 100 of the tibial trial determines the correctorientation for fitting of the femoral prosthesis on the femur.

[0152] As an alternative, rather than cutting the channel into the femuras described above, a marker pen or diathermy can be used in place ofthe saw blade for marking of the femoral condyle for subsequent cuttingof the channel into the femur using a saw blade in a free hand manner.

[0153] With the knee in full extension, and with care being taken not tohyperextend the knee, an imaginary line aligned with the groove 100 ofthe tibial trial is projected from the anterior side of the tibial trial98 to the corresponding femoral medial condyle as indicated in FIG. 20.The point 114 at which the line strikes the femur is marked andcorresponds to the optimal position of the anterior edge 116 of thefemoral prosthesis 2, and is indicated more clearly in FIG. 21 where thetibia is shown in flexion relative to the femur.

[0154] A femoral sizer 118 is then aligned with the channel cut into thefemur, with the posterior end 120 of the femoral sizer positionedflushly against the resected posterior face 122 of the femoral condyle,to allow determination of the required size of femoral prosthesis 2 bycomparing the position of the mark 114 with calibrated markings on thefemoral sizer as shown in FIG. 22.

[0155] The femoral condyle can then be sculpted as required toaccommodate the fitting of the femoral prosthesis 2. This can be readilyachieved with the use of a cutter device such as a femoral shaping rasp124 illustrated in FIG. 23 or for instance, a router having a rotatablecutter for resecting bone from the femur. As can be seen, the rasp 124has a tang 126 for being received by a reciprocating power saw. The body128 of the rasp is generally flat and is provided with a tapered leadingend 130. A key (not shown) extends centrally along the base of the raspfor reception in the guide groove 100 of the tibial trial 98.Accordingly, the groove of the tibial trial 98 acts to guide thereciprocating motion of the rasp when positioned on the tibial trialunder the femur as illustrated in FIG. 23.

[0156] As will be understood, to sculpt the femur, the tibia is rotatedabout the femur through an arc of motion between forward and backwardpositions during which movement the cutting face of the rasp acts toprogressively shave away the required thickness of the femur. It willalso be appreciated that the thickness of the rasp is such to ensurethat the original spacing between the femur and the tibia provided bythe selected spacer 28 will be essentially retained upon the femoralprosthesis being fitted, for substantially maintaining the optimisedbalance in ligaments and other soft tissue initially provided by thespacing of the femur from the tibia by the selected spacer.

[0157] Drilling of the required bore 132 into the femur for reception ofthe peg 18 of the femoral prosthesis is readily achieved using a femoralpeg drill guide 134 carrying a guide bracket 136 having a correspondingshape to the femoral prosthesis. Determination of the position fordrilling the bore 132 is achieved by aligning the anterior tip 138 ofthe guide bracket 136 over the location 114 determined on the femur tocorrespond with the optimal positioning of the anterior end of thefemoral prosthesis and reference is drawn to FIG. 24 for explanatorypurposes.

[0158] Subsequently, the joint space is lavaged and a femoral trialaffixed to the femur for a final assessment of joint stability and jointkinematics.

[0159] The tibial and femoral trials are then removed and the jointspace thoroughly cleaned using pulsatile lavage prior to the tibialprosthesis 10 and the femoral prosthesis 2 being fixed to the tibia andthe femur respectively, using appropriate conventionally known bondingcement such as polymethylacrylate bone cement. Prior to closing thewound the joint space is again thoroughly lavaged and if deemednecessary, local anaesthetic may be infiltrated at the wound site toassist post operative pain relief.

[0160] As will be appreciated, the tibial prosthesis used in a method asdescribed herein may be selected from a number of such prostheses with adifferent thickness T to each other. The selected prosthesis will ofcourse depend on the thickness of the spacer 28 required to initiallyoptimise tension and balance in the action of the relevant ligaments andsoft tissue structures of the knee joint during the movement of thetibia about the femur between forward and backward positions. For eachthickness of tibial prosthesis, a corresponding cutting block 38 forguiding cutting of the tibia and the femur at the required spacing toaccommodate the selected tibial prosthesis will be provided.Alternatively, a cutting block able to be adjusted to alter the spacingbetween the guide slots 60 and 62 as necessary to correspond to thethickness T of the selected tibial prosthesis may be used.

[0161] Another embodiment of a tibial trial 98 having a guide channel140(a) extending part way across the tibial trial in a generallyanteroposterior direction is shown in FIG. 25 for reception of a router.The channel 140(a) has a dove tailed cross-section lying in a planeextending perpendicularly with respect to the major axis of the tibialtrial. An identical channel 140(b) is defined in the underside of thetibial trial. As can be seen, this tibial trial is again provided with achannel 142 which extends from the upperside face 140 of the tibialtrial through to its base 146 for reception of an obliquely orientatedtrocar pin therein for securing the tibial trial to the tibia. A furtherchannel 148 is defined on the opposite side of the tibial trial forreception of an obliquely directed trocar pin. Indeed, the tibial trialis designed such that the tibial trial may be secured to either themedial condyle or the lateral condyle following the resection of bonetherefrom. That is, by simply rotating the tibial trial 180° about itsmajor axis the trial can be pinned to either medial lateral resectedsurfaces 96 of the tibia by the insertion of trocar pins throughchannels 142 and 148. The tibial trial when secured in position on thetibia prior to receiving the router is shown in FIG. 26.

[0162] The router 150 shown in FIG. 27(a) comprises a flat head 152having a substantially constant thickness along its length and which isdetachably connected to body 154 of the router. A cutter disk 156 isseated in an aperture defined in the upperside 158 of the router head152. A forward guard 160 is defined on the leading end 162 of therouter. An end view of the router is shown in FIG. 28 and a side view inFIG. 29. As can be seen, a boss 164 having a dove tailed profilecorresponding to that of the guide channel 140(a) of the tibial trial ofFIG. 25 depends from the underside of the router 150 for reception inthe guide channel 140(a) for thereby inhibiting lifting of the routerfrom the tibial trial.

[0163] The cutter disk 156 is more clearly shown in FIG. 27(b) and has adished upper surface 165 and a plurality of radially directed blades166. Each blade decreases in thickness from a leading cutting edge 168to a trailing edge 170. A further cutting edge 172 is defined at theouter peripheral end of each blade. In addition, an integrally formedupstanding cutting blade 174 is centrally located on the cutter disk.The upstanding blade 174 has a plurality of upwardly directed cuttingedges 176 spaced at 120° intervals around the blade. Specifically, thecutting edges 176 are defined on both the side and top end of theupstanding blade as can be seen.

[0164] Turning now to FIG. 30(a), the cutter disk 156 furtherincorporates an integrally formed drive gear 178 with a plurality ofvertically orientated teeth 180 which mesh with the screw of the screwdrive 182 rotatably received within the head 152 of the router 150.

[0165] The cutter disk 156 has an internal female thread which mateswith a screw 186 extending through collet 188 received in recess 190defined in the underside of the router head, such that the cutter disk156 is thereby retained in position on the router head and is rotatablewith respect to the router head.

[0166] A drive shaft 192 is rotatably mounted within the router body andprojects therefrom for engagement with the female bayonet coupling 194of the screw drive 184 of the router head. As shown in FIG. 30(b), theprojecting end 196 of the drive shaft 192 carries bayonet pin 198 forreception in the bayonet recesses 200 of the bayonet coupling forthereby locking the router head 152 to the router body 154. Theprojecting end 196 of the drive shaft 192 is further provided with aflat drive projection 202 which slots into the slot 204 of the bayonetcoupling for driving rotation of the screw drive 184 and so causingrotation of the cutter disk 156. The router body is adapted for beingcoupled with a power drive for driving rotation of the cutter disktypically in the range of from 5,000 rpm to about 7,000 rpm. As will beunderstood, once used, the router head 152 may be removed and discarded.Desirably, however, the body 154 of the router is sealed and is reusablefollowing sterilisation.

[0167] Rather than engaging the cutter disk directly, the screw drive184 of other embodiments may be arranged to drive a gear arrangementcomprising a single gear or for instance a gear train incorporating anumber of gears for driving the cutter disk. Alternatively, the routermay incorporate a drive in the form of an endless belt, band or the likewhich upon being driven by the drive shaft causes rotation of the cutterdisk.

[0168] As indicated above, the cutter disk 156 is freely rotatable withrespect to the head of the router and may be lifted from the head uponthe screw 186 being removed to allow replacement of the cutter disk withanother of the same or different design. A blunt cutter disk may resultin thermal necrosis of bone of the femur and accordingly it is desirableto replace the cutter disk if necessary. To assist in the insertion ofthe router into the knee joint, the leading end 162 of the head of therouter has an arcuate profile.

[0169] The insertion of the router into the knee joint is indicated inFIGS. 31 and 32, and the use of the tibial trial of FIG. 26 and router150 in unicondylar knee arthroplasty is illustrated in FIGS. 33(a) to33(c). Specifically, the tibia is again placed in flexion with respectto the femur, and the boss 164 of the router is inserted into the guidechannel 140(a) of the tibial trial as shown in FIG. 32. Upon operationof the router and the tibia being moved about the femur through an arcof motion to an extended position, bone is resected from the femur tothe desired depth in the direction of movement of the tibia as shown inFIG. 33(b). As indicated more clearly in FIG. 33(c), the channel 206 forreception of the central fin 16 of the femoral prostheses issimultaneously cut into the femoral condyle by upstanding blade 174 ofthe cutter disk 156 of the router 150.

[0170] Rather than cutting the channel 206 for reception of the centralfin of the femoral prosthesis simultaneously with the resurfacing of thefemur utilising the cutter disk 156, the resurfacing of the femur andthe cutting of the channel 206 may be achieved in a two stage process.That is, a cutter blade may be located in the router for cutting thechannel in an initial step, and then that cutter blade replaced with onefor resecting the required thickness of bone from the femur and whichincorporates an upstanding centrally located non-cuffing boss forreception in the cut channel 206 to thereby guide the resurfacing of thefemur. In this instance, the boss will generally be of a height suchthat a space remains between the upper end of the boss and the overlyingroof of the channel.

[0171] Similarly, rather than resecting the posterior chamfer from thefemur with a reciprocating saw utilising the cutting block 38 forguidance, the posterior chamfer may be resected from the femur with theuse of a router 150 in which the router head 152 is provided without aguard 160. As such, a cutting block may be provided that while beingcapable of being coupled with the spacer selected for optimum spacing ofthe femur from the tibia as described above, may only be adapted forguiding cutting of the tibia at the relevant depth therein and not thefemur.

[0172] While the method has been described in relation to arthroplastyperformed on the medial condyles of the tibia and the femur, unicondylararthroplasty may be performed on the lateral condyles in the samemanner.

[0173] In addition, rather than removing the entire upper segment of therelevant condyle of the tibia in unicondylar arthroplasty to provide anexposed recess on which the tibial trial and subsequently the finaltibial prosthesis 10 is onset and fixed in position as described above,a recess may be formed in the condyle into which the tibial trial andultimately the tibial prosthesis are inset, respectively. An apparatusfor providing such a recess in the tibia is shown in FIG. 34.

[0174] The apparatus comprises a router 208 and a guide jig 210 forguiding the router to form the inset recess 212, in this case in themedial condyle of the tibia 14.

[0175] The router 208 has an elongated body 214 housing a drive shaft216 for driving rotation of a router blade 218 in the same manner asdescribed for the router shown in FIG. 30, for resecting the bone fromthe tibia to the desired depth in the tibia. The drive shaft 216projects from the trailing end 222 of the body 214 for reception by apower tool for driving rotation of the drive shaft.

[0176] A guide pin 224 projects from an underside of the router body 214for reception in a recessed template 226 defined in the floor of channel228 of the guide jig 210. A recessed area is also defined in the body ofthe router to allow the router to overlie the rim 232 of the recess andto allow the router blade to resect the bone from the tibia to thedesired depth. The guide pin has a length to ensure reception in therecessed template of the guide jig when the router is positioned overthe tibia prior to commencement of the resection of bone in theformation of the recess. Similarly, the depth of the recessed templateis sufficient to ensure the entire exposed length of the guide pin isable to be accommodated therein.

[0177] The profile of the template 226 substantially matches theexternal profile of the tibial trial to be used, and the template isdimensioned for the recess to be of a size sufficient to allow thetibial trial to be seated on the resected tibial surface 96 at the baseof the recess. Once received in the recess, the surrounding bone of thetibia acts to inhibit the tibial trial and subsequently the actualtibial prosthesis 10 from being transversely dislocated.

[0178] In order to position the guide jig 210 about the knee, thetibiofemoral cutting block 38 is firstly arranged adjacent to the tibiain the manner described above utilising the selected spacer 28 todetermine the position of the cutting block with respect to the tibia,prior to the securing of the cutting block in position using trocar pins234. As will be understood, trocar pins 234 are dimensioned for beinginserted into the channels 84 and 90 of the cutting block and alignmentcomponent in a sliding fit and to allow the cutting block and alignmentcomponent 68 to be slid from the pins following resection of the one orboth of the tibia and femur as described above.

[0179] Once the cutting block and spacer assembly has subsequently beenslid from the trocar pins the guide jig 210 is slid onto the trocar pins234 such that the trocar pins are received in longitudinally extendingparallel channels 236 of the guide jig.

[0180] The router blade 218 projects from the head 220 of the router adistance such that when the router is received in the channel 228 of theguide jig, bone is able to be resected from the tibia to a depthcorresponding to the position of the bottom 72 of the lower slot 64 ofthe cutting block 38 prior to removal of the cutting block from thetibia. Resection of bone from the tibia beyond this depth is inhibitedby abutment of the underside surface 238 of the rear end region 240 ofthe router with the floor 242 of the channel of the guide jig. To resectbone from the tibia to greater depths to accommodate different sizedtibial trials, different sized router blades may be utilised on therouter.

[0181] In order to enhance stability, the guide jig is provided with arest 244 that projects downwardly from the leading end 246 of the guidejig and which rests against the leg of the patient to thereby assist inmaintaining the jig in position at the angle in the anterior toposterior direction determined by the alignment component 68. The guidejig is secured in position on the tibia by pin 248 inserted into thetibia through channel 250 defined in the rest 244 which channel extendsat an oblique angle with respect to parallel channels 236 of the guidejig receiving trocar pins 234.

[0182] The recess 212 in the tibia is formed and shaped by theapplication of downward pressure to the router as the router is movedside to side and forward and backward in the guide jig, the movement ofthe router across the tibia being limited by the restricted field ofmovement of the guide pin in the recessed template of the jig.Accessible tibial osteophytes may be removed prior to or following theformation of the recess in the tibia. To allow for the resection ofdifferently sized recesses, a range of guide jigs may be provided withtemplates of different width and length dimensions. Similarly, thelocation of the guide pin 224 on the router may be adjustable along therouter to accommodate resection of the recess in the desired position onthe tibia, or otherwise the guide jig may be adapted for facilitatingadjustment of the position of the guide jig along the trocar pins. Thismay be achieved for instance by the rest being extendible relative tothe remainder of the guide jig for causing the desired displacement ofthe template away from the knee joint.

[0183] The tibia trial when seated in the recess will typically protrudeabove the rim 232 of the recess. Usually, the tibial trial will besecured in position in the recess by an appropriately located pininserted into the tibia at an oblique angle (not shown).

[0184] The channel for receiving the central fin 16 of the femoralprosthesis may then be cut into the corresponding condyle of the femurif not already achieved simultaneously during the resection of the femurwith the use of a router of the type shown in FIG. 30.

[0185] Rather than utilising a guide jig arrangement of the type shownin FIG. 34 for resecting a channel into the tibia for insertion of atibial trial and subsequently a tibial prosthesis therein, apparatus asshown in FIG. 8 may more desirably be utilised. In this instance, ratherthan the cutting block 38 being mounted on the rearward tongue 66 of thealignment component 68, the cutting block is rotated 180° and mounted onthe forward tongue 76 of the alignment component as indicated in theexploded view shown in FIG. 35 and the view of the assembled arrangementindicated in FIG. 36. Accordingly, in this instance the alignmentcomponent 68 is located between the cutting block 38 and the tibia 14for resection of the posterior chamfer from the femur 6 as indicatedabove. Once the posterior chamfer has been resected, the cutting block38 is slid from the alignment component 68 leaving the alignmentcomponent 68 behind in position relative to the tibia.

[0186] The body 74 of the alignment component is dimensioned such thatthe upper surface 252 of the head 254 is aligned at the same level asthe bottom of the middle slot 62 of the cutting block for the spacer,prior to the cutting block being slid from the trocar pins securing thealignment component in position relative to the tibia. The upper surface252, therefore, may therefore be used as a rest for a router 256 asshown in FIG. 37 for removing bone from the tibia to form a recess tothe desired depth for the seating therein of a tibial trial andthereafter the ultimate tibial prosthesis. That is, the height of thecutter blade 258 of the router 256 is dimensioned such that the floor ofthe recess resected into the tibia is at a level corresponding to thelevel of the bottom 72 of the lower slot 64 of the cutting block whenlocated in position adjacent to the tibia. As with the cutter blade ofthe router shown in FIG. 30, the cutter blade 258 has cutting edgesdefined on both the sides and top end of the blade.

[0187] The correct size of the recess to be resected is firstlyascertained by locating different tibial trial templates on the tibialcondyle and selecting the most appropriate one prior to marking theprofile of the selected templated on the tibial trial in the requiredlocation with methylene blue or other suitable dye as is conventionallyknown in the art.

[0188] Following removal of the alignment component 68 for insetting ofthe tibial trial in the resected recess, the femur may be furtherresected as described above for the fitting of the femoral prosthesis.

[0189] Another router employing a cutter disk 260 is shown in FIG. 38.This embodiment rather than being adapted for reception by a tibialtrial, has a body 262 with a head 264 adapted for being seated on thebase of the recess 212 resected into the tibia and which is dimensionedsuch that movement of the router when in position in the recess in agenerally medial to lateral direction or vice versa is limited. Thecutter disk is the same as that utilised on the router shown in FIG. 30and is arranged for resection of the femur to the desired depth in thatbone in the manner described above upon movement of the tibia through anarc of motion about the femur.

[0190] In a bicondylar knee arthroplasty method, two small stabincisions are made in the knee with a scalpel blade to provide portalsfor insertion of a spacer in each one, respectively. The incisions arelocated medial and lateral to the patellar tendon to allow access tobetween the tibia and the femur, and are positioned so as to generallynot coincide with ligamentous and other soft tissue structures of theknee.

[0191] A spacer is then introduced between the opposing lateral condylesand the opposing medial condyles of the tibia and the femur,respectively. The desired thickness of spacers required to obtainbalance in the action of relevant ones of the ligaments and other softtissue structures of the knee during flexion and extension of the tibiarelative to the femur to provide appropriate tension in the knee jointand correction of varus or valgus deformity is determined substantiallyas described above using different thicknessed spacers.

[0192] Specifically, the tibia is moved about the femur between forwardand backward positions and the kinematics of the knee evaluated. Ifnecessary, one or both of the spacers may be substituted with one(s) ofa different thickness and movement of the knee joint while the spacersare in position checked again. This may be repeated a number of timesuntil the optimum spacing of the femur from the tibia is obtained.Accordingly, the spacers selected for optimum spacing of the femur fromthe tibia may have the same thickness as each other or a differentthickness to each other depending on the degree of spacing requiredbetween the respective condyle pairs.

[0193] The spacers will usually be linked together by a cross-bar duringthe rotation of the tibia about the femur. The cross-bar may comprise astiff metal member secured to each spacer by a clamp or suitablefastener respectively, or other such arrangement for inhibitingindependent movement of the spacers.

[0194] In this way, the desired balancing and deformity correction ofthe knee joint may be achieved prior to surgically opening the medialand lateral compartments of the knee joint for resection of the medialand lateral condyles of the femur and the tibia.

[0195] Once the spacers for providing the optimum spacing of the femurand the tibia have been selected, unicondylar arthroplasty is performedon each of the medial and lateral condyle pairs as described above, onepair at a time. Preferably, the condyle pair deemed to require thegreater degree of deformity correction is subjected to arthroplastyfirst.

[0196] More particularly, bone may be resected from the tibia utilisingeither the tibiofemoral cutting block 38 or guide jig 210 to guide theresection of the bone. Once both the tibial and femoral trials have beenfitted, arthroplasty is then performed on the other of the condylepairs.

[0197] Prior to doing so, the spacer selected for spacing of thosecondyles apart is reinserted between them and the kinematics of the kneejoint checked by rotating the tibia about the femur to confirmsatisfactory kinematics of the knee joint. Bone is then resected fromthe tibial and femoral condyles of that pair to the desired depth ineach one again utilising the spacer as reference for the positioning ofthe tibiofemoral cutting block 38 or guide jig 210. Upon fitting of thefurther tibial and femoral trials, the kinematics of the knee joint arechecked once again to ensure adequate range of motion and retention ofoptimum tension in ligaments and other soft tissue structures of theknee joint. The respective tibial trials and femoral trials aresubsequently removed and replaced with the final tibial and femoralprostheses. Generally, the tibial and femoral prostheses will be fittedto one condyle pair at a time.

[0198] Accordingly, the bicondylar knee arthroplasty method describedcomprises performing unicondylar knee arthroplasty as described hereinon both medial and lateral condyle pairs of the knee. As will be furtherappreciated, the bicondylar arthroplasty method involves gentlyretracting the patella transversely about the knee joint to gain accessto the medial or lateral compartment of the knee joint and, subsequentlyretracting the patella transversely about the knee joint in the oppositedirection to gain access to the other of the knee compartments. Themethod may also allow the quadricep system to remain substantiallyintact.

[0199] Moreover, as with the unicondylar arthroplasty techniquedescribed, the bicondylar knee arthroplasty method may allow the desiredtensioning and deformity correction to be achieved substantially withoutthe need to transect, elevate or release soft tissue structures of theknee joint although again, adjustment prior to or following fitting ofthe tibial and femoral trials is not excluded.

[0200] Accordingly, although the present invention has been describedhereinbefore with reference to preferred embodiments, the skilledaddressee will understand that numerous variations and modifications arepossible without departing from the scope of the invention.

We claim:
 1. A method of arthroplasty on a joint comprising first andsecond bones, said method comprising the steps of: (a) obtaining adesired spacing of said first and second bones; (b) determining depth ofbone to be resected from at least one of said first and second bones toenable fitting of at least one prosthesis selected from a plurality ofprostheses; (c) resecting bone from one or both of said first and secondbones substantially to the determined depth in the or each one,respectively; and (d) fitting the or each said prosthesis.
 2. A methodaccording to claim 1 further comprising: selecting at least one spacerfor providing the desired spacing of said first bone from said secondbone; and positioning the spacer in the joint between the first andsecond bones to thereby obtain the desired spacing of said first bonefrom said second bone.
 3. A method according to claim 2 wherein theselecting comprises: (i) choosing the spacer from a range of spacers forproviding different spacings of the first bone from the second bone,respectively; (ii) moving the second bone about the first bone throughat least a portion of a range of motion between partially flexed andextended positions to evaluate movement of the joint while the chosensaid spacer is in position between the first and second bones.
 4. Amethod according to claim 3 wherein the selecting further comprisesrepeating steps (i) and (ii) as necessary to obtain the desired spacingof the first bone from the second bone using a different spacer chosenfrom the range of spacers each time.
 5. A method according to claim 2further comprising placing the joint in a position of flexion wherebythe second bone is arranged at an angle with respect to the first bonefor the resection of the bone.
 6. A method according to claim 2 furthercomprising: locating a guide jig in position about the joint for guidingthe resection of the bone; and using the guide jig to guide cutting ofthe second bone substantially at the desired depth in a medial tolateral or lateral to medial direction in the resection of bone from thesecond bone.
 7. A method according to claim 6 wherein the locating ofthe guide jig comprises utilising the spacer as a reference to determinethe position of the guide jig about the joint for guiding the cutting ofthe second bone substantially at the desired depth.
 8. A methodaccording to claim 6 wherein the locating of the guide jig comprisescoupling the guide jig with the spacer while the spacer is positioned inthe joint between the first and second bones to thereby determine theposition of the guide jig about the joint.
 9. A method according toclaim 6 further comprising using the guide jig to guide cutting of thefirst bone.
 10. A method according to claim 6 further comprising:locating a cutter device in position in the joint between the first andsecond bones; and moving the second bone through at least a portion of arange of motion about the first bone between partially flexed andextended positions while the cutting device is being operated andlocated between the first and second bones, to thereby substantiallyremove bone substantially to the desired depth from the first bone in adirection of travel of the second bone relative to the first bone.
 11. Amethod according to claim 10 further comprising: removing the guide jigfrom said position about the joint; and inserting a trial implant inposition in a recess in the second bone formed by the resection of thebone from the second bone; wherein the trial implant is adapted forreception of the cutter device thereon and maintaining the cutter devicein a desired orientation with respect to the first bone as the secondbone is moved through the range of motion between the flexed andextended positions.
 12. A method according to claim 11 furthercomprising placing the cutter device on the trial implant such that thetrial implant and the cutter device are coupled together prior to movingthe second bone through the range of motion.
 13. A method according toclaim 1 further comprising: cutting a channel into either the first orsecond bone for reception of an upstanding fin of a selected prosthesis,wherein the channel when formed lies in an anterior to posteriordirection.
 14. A method according to claim 10 further comprising:cutting a channel into the first bone utilising the cutter device forreception of an upstanding fin of a selected said prosthesis; whereinthe channel is cut into the first bone simultaneously with the resectionof the bone from the first bone to the desired depth as the second boneis moved through the range of motion about the first bone.
 15. A methodaccording to claim 1 wherein the joint is a knee and said first andsecond bones are the femur and tibia, respectively.
 16. A methodaccording to claim 15 wherein the bone is resected from a lateral ormedial condyle of the tibia and a corresponding condyle of the femur.17. A method according to claim 16 further comprising resecting bonefrom the other condyle of the tibia and the condyle of the femurcorresponding to the other tibial condyle.
 18. A method according toclaim 15 wherein the bone is resected from a lateral or medial condyleof the tibia only.
 19. A method of arthroplasty on a knee joint,comprising the steps of: (a) surgically providing access to the kneejoint; (b) selecting at least one spacer for providing a desired spacingof the femur from the tibia; (c) positioning the selected spacer in theknee joint to obtain the desired spacing of the femur from the tibia;(d) using the spacer as a reference to determine a location on each oneof the tibia and the femur indicating depth of bone to be resected fromeach for fitting of chosen tibial and femoral prostheses; (e) cuttingthe tibia and the femur substantially at the determined location on eachfor resection of the bone from each one to the required said depth fromeach one, respectively; and (f) fitting the chosen tibial and femoralprostheses.
 20. A method according to claim 19 wherein the selecting ofthe spacer comprises: (i) choosing the spacer from a range of spacersfor providing different spacing of the femur from the tibia,respectively; and (ii) moving the tibia about the femur through at leasta portion of a range of motion between partially flexed and extendedpositions to evaluate movement of the knee joint while the chosen saidspacer is in position between the femur and the tibia.
 21. A methodaccording to claim 20 wherein the selecting further comprises repeatingsteps (i) and (ii) as necessary to obtain the desired spacing of thefemur from the tibia using a different spacer from the range of spacerseach time.
 22. A method according to claim 19 further comprising placingthe knee joint in a position of flexion whereby the tibia is arranged atan angle with respect to the femur for the resection of the bone.
 23. Amethod according to claim 19 wherein the cutting of the femur comprisesresecting a portion from the posterior of the femur.
 24. A methodaccording to claim 19 further comprising: locating a cutting device inthe knee joint between the femur and the tibia; and moving the tibiathrough a range of motion about the femur between partially flexed andextended positions while the cutting device is being operated to therebyremove bone substantially to the desired depth from the femur in adirection of travel of the tibia relative to the femur.
 25. A methodaccording to claim 19 further comprising: cutting a channel into eitherthe femur or the tibia for reception of an upstanding fin of the femoralprosthesis, wherein the channel when formed lies in an anterior toposterior direction.
 26. A method according to claim 24 furthercomprising: cutting a channel into the femur utilising the cutter devicefor reception of an upstanding fin of the femoral prosthesis,simultaneously with the resection of the bone from the femur as thetibiais moved through the range of motion about the femur.
 27. A methodaccording to claim 19 wherein the bone is resected from a lateral ormedial condyle of the tibia and a corresponding condyle of the femur.28. A method of arthroplasty on a knee joint, comprising the steps of:(a) locating a cutting device in position in a knee joint between thefemur and the tibia; and (b) moving the tibia through a range of motionabout the femur between at least partially flexed and extended positionswhile the cutting device is being operated to thereby remove bonesubstantially to a desired depth from the femur in a direction of travelof the tibia relative to the femur, for enabling fitting of a femoralprosthesis to the femur.
 29. A method according to claim 28 furthercomprising: resecting bone from the tibia to a desired depth to providea prepared surface for placement of a tibial implant or trial; fixingthe tibial implant or trial in position on the prepared surface of thetibia, and placing the cutter device on the tibial implant or trialprior to moving the tibia through the range of motion about the femur.30. A method according to claim 29 wherein the tibial implant or trialis adapted for mating with the cutter device and the placing of thecutter device on the tibial implant or trial comprises mating the tibialimplant or trial and the cutter device together such that the cutterdevice is maintained in a desired orientation with respect to the femuras the tibia is moved through the range of motion between the flexed andextended positions.
 31. A method according to claim 29 wherein theresection of bone from the tibia comprises cutting the tibiasubstantially at the desired depth to thereby provide the preparedsurface for placement of the tibial implant.
 32. A method according toclaim 28 wherein the resection of the bone comprises forming a recess inthe tibia in which the tibial implant is disposed in position in therecess.
 33. A method according to claim 28 further comprising forming arecess in the uppermost end of the tibia to a desired depth forreception of the cutting device for removing the bone to the desireddepth from the femur.
 34. A method according to claim 28 furthercomprising cutting a channel into either bone utilising the cuttingdevice for reception of an upstanding fin of the femoral prosthesis,wherein the channel is cut into said bone simultaneously with theresection of the bone from the femur as the tibia is moved through therange of motion about the femur.
 35. A method of determining theposition of a guide jig about a knee joint for subsequently guidingcutting of one or both of the tibia and the femur at a desired depth ineither one respectively, the method comprising: (a) locating a selectedspacer in the knee joint to obtain a desired spacing of the femur fromthe tibia; and (b) arranging the guide jig and the spacer together tothereby determine the position of the guide jig about the knee joint forguiding the cutting of either one of the tibia and the femur.
 36. Amethod according to claim 35 wherein the spacer is selected from a rangeof spacers and the selecting of the spacer comprises: (i) choosing thethickness of the spacer from a range of spacer thicknesses for providingdifferent spacings of the femur from the tibia, respectively; (ii)moving the tibia about the femur through a range of motion between atleast partially flexed and extended positions to evaluate movement ofthe knee joint while the selected spacer is in position between thefemur and the tibia.
 37. A method according to claim 36 wherein theselecting further comprises repeating steps (i) and (ii) as necessary toobtain the desired spacing of the femur from the tibia using a differentspacer thickness chosen from the range of spacer thicknesses each time.38. A method according to claim 35 wherein the arranging of the guidejig with the spacer comprises coupling the guide jig and the spacertogether.
 39. A method according to claim 38 wherein the coupling of theguide jig with the spacer comprises sliding the guide jig onto aprotruding end region of the spacer protruding from the knee joint. 40.A method according to claim 35 further comprising: coupling the guidejig with an alignment component for aligning the guide jig relative tothe knee joint at a desired angle in an anterior to posterior directionof the knee joint; and securing the guide jig in said position such thatthe guide jig is aligned at the desired angle.
 41. A method according toclaim 40 wherein the alignment component is capable of being withdrawnfrom the guide jig leaving the guide jig behind secured in said positionabout the knee joint.
 42. A method according to claim 40 wherein thealignment component for aligning the guide jig at the desired angle isarranged between the knee joint and the guide jig when the guide jig issecured in said position at the desired angle.
 43. A method according toclaim 35 further comprising: arranging the guide jig in a desired medialto lateral orientation with respect to the knee joint.
 44. A methodaccording to claim 43 wherein the arranging of the guide jig in thedesired medial to lateral orientation comprises utilising an alignmentguide for aligning the guide jig with respect to the tibia.
 45. A guidejig for use in a method of arthroplasty on a knee joint of a patient,wherein the guide jig is adapted for guiding cutting of at least one ofthe tibia and the femur in resection of bone therefrom for enablingfitting of one or both of a tibia and a femoral prosthesis, and whereinthe guide jig is further adapted for being arranged with a selectedspacer for spacing the femur from the tibia and for being secured aboutthe knee joint in a position determined by the spacer to guide cuttingof at least one of the tibia and the femur, respectively, substantiallyat a desired depth.
 46. A guide jig according to claim 45 wherein theguide jig is adapted for receiving the spacer for thereby determiningthe position of the guide jig about the knee joint.
 47. A guide jigaccording to claim 46 wherein the guide jig has a through passageway forreception of the spacer for thereby determining the position of theguide jig about the knee joint.
 48. A guide according to claim 45wherein the guide jig is adapted for guiding cutting of the tibia whensecured about the knee joint is said position.
 49. A guide jig accordingto claim 45 wherein the guide jig is adapted for guiding cutting of boththe tibia and the femur.
 50. A guide jig according to claim 48 whereinthe guide jig is adapted for guiding the cutting of the tibia and thefemur at a fixed predetermined spacing from one another, respectively.51. A guide jig according to claim 45 wherein the guide jig is adaptedfor guiding the cutting of at least one of the tibia and the femursubstantially in a medial to lateral or lateral to medial direction whensecured about the knee joint in said position.
 52. A guide jig accordingto claim 51 wherein the guide jig is a cutting block with a through slotfor guiding the cutting of the tibia.
 53. A guide jig according to claim52 wherein the guide jig has a further through slot for guiding thecutting of the femur.
 54. A guide jig according to claim 45 wherein theguide jig is further adapted for guiding cutting in a direction alongthe tibia for removing a segment of bone from the tibia.
 55. A guide jigaccording to claim 54 wherein the guide jig is provided with at leastone channel for guiding the cutting along the tibia for removing aportion of the segment of bone and extending from front through to therear of the guide jig.
 56. A guide jig according to claim 55 wherein theguide jig is provided with a pair of spaced apart said channels, onechannel being defined in each one of opposite side regions of the guidejig, respectively.
 57. A guide jig according to claim 55 wherein the oreach said channel slopes inwardly at a desired angle with distance froman upperside to an opposite underside of the jig.
 58. A guide jigaccording to claim 45 wherein the guide jig is adapted for guiding thecutting of the tibia to provide a tibial surface sloping downwardly inan anterior to posterior direction of the knee joint when secured inposition about the knee joint.
 59. An alignment device for aligning aguide jig in position about a knee joint for guiding cutting of at leastone of the tibia and the femur at a desired location on the or each onerespectively during arthroplasty on the knee joint, and comprising: abody for receiving the guide jig and coupling the guide jig with analignment guide for aligning the guide jig in a desired medial tolateral orientation with respect to the knee joint; and wherein the bodyis adapted for aligning the guide jig at a desired angle in an anteriorto posterior direction of the knee joint and for securing of the guidejig at the desired angle prior to removal of the body from about theknee joint for allowing cutting of the one or both of the tibia and thefemur to be guided by the guide jig.
 60. An alignment device accordingto claim 59 wherein the body is adapted for aligning the guide jig at adownward said angle in the anterior to posterior direction.
 61. Analignment device according to claim 59 wherein the body is adapted forbeing coupled with the guide jig for aligning the guide jig in positionabout the knee joint.
 62. An alignment device according to claim 59wherein the body is adapted for being arranged between the guide jig andthe alignment guide for enabling the alignment guide and the body to beremoved from about the knee joint while the guide jig remains behind inposition about the knee joint.
 63. An alignment device according toclaim 59 wherein the body incorporates a first mating mechanism forbeing received by the guide jig and facilitating the alignment for theguide jig in the anterior to posterior direction.
 64. An alignmentdevice according to claim 63 wherein the first mating mechanism isarranged for projecting toward the knee joint when the body is receivedby the guide jig and the guide jig is secured about the knee at thedesired angle.
 65. An alignment according to claim 63 wherein the bodyincorporates a second mating mechanism for reception by the alignmentguide for achieving the coupling of the body and the alignment guide,and wherein the second mating mechanism is arranged for projecting awayfrom the knee.
 66. An alignment device according to claim 59 wherein thebody is further adapted for allowing reception of a selected spacerprojecting from between the tibia and the femur by the guide jig whilethe guide jig is received by the body and aligned at the desired anglerelative to the knee joint.
 67. An alignment device for supporting acutting device for resecting bone from the tibia to a desired depth toform a recess in the tibia during arthroplasty on a knee joint, andcomprising: a body for receiving a guide jig for guiding cutting of thetibia and coupling the guide jig with an alignment guide for aligningthe guide jig in a desired medial to lateral orientation with respect tothe knee joint; and wherein the body is adapted for aligning the guidejig at a desired angle relative to the knee joint in an anterior toposterior direction and for being secured about the knee joint in aposition determined by the guide jig for supporting the cutting devicefollowing removal of the guide jig from the body.
 68. An alignmentdevice according to claim 67 wherein the body is adapted for aligningthe guide jig at a downward said angle in the anterior to posteriordirection of the knee.
 69. An alignment device according to claim 67wherein the body is adapted for being coupled with the guide jig foraligning the guide jig in position about the knee joint.
 70. Analignment device according to claim 67 wherein the body incorporates afirst mating mechanism for being received by the guide jig andfacilitating the alignment of the guide jig.
 71. An alignment deviceaccording to claim 70 wherein the first mating mechanism is arranged forprojecting away from the knee joint when the body is located about theknee joint.
 72. An alignment device according to claim 70 wherein thebody incorporates a second mating mechanism for reception by thealignment guide for achieving the coupling of the body and the alignmentguide, and wherein the first mating mechanism overlies the second matingmechanism.
 73. A spacer for being inserted into a knee joint to providea desired spacing of the femur from the tibia in arthroplasty on theknee joint, comprising an elongate member with a leading end regionadapted for being inserted between the tibia and the femur to therebyobtain the desired spacing of the femur from the tibia, and an oppositeend region adapted for coupling with a guide jig for guiding the cuttingof the or each one of the tibia and the femur in the resection of thebone.
 74. A spacer according to claim 73 wherein the leading end regionof the spacer is adapted for retaining the spacer in the knee joint. 75.A spacer according to claim 73 wherein the leading end region of thespacer is adapted for receiving the medial or lateral condyle of thefemur for thereby retaining the spacer in the knee joint.
 76. A spaceraccording to claim 74 wherein a concave trough is defined in the leadingend region of the spacer for receiving the medial or lateral condyle ofthe femur and thereby retaining the spacer in the knee joint.
 77. Aspacer according to claim 76 wherein a raised ridge orientated in adirection across the spacer is defined on the leading end region, andthe leading end region is scooped forward of the ridge thereby definingthe concave trough for reception of the medial or lateral condyle of thefemur.
 78. A spacer according to claim 73 wherein the leading end regionof the spacer has an upperside and an opposite underside, and aprotuberance for being seated on an articulating surface of the tibia isdefined on the underside for providing the desired spacing of the femurfrom the tibia.
 79. A spacer according to claim 78 wherein theprotuberance is a bulbous protuberance for being seated on a low regionof the tibia under the medial or lateral condyle of the femur.
 80. A setof spacers for allowing selection of at least one of the spacers forinsertion into a knee joint to provide a desired spacing of the femurfrom the tibia in arthroplasty on the knee joint, each said spacerrespectively comprising a leading end region adapted for being insertedbetween the tibia and the femur to thereby space the femur from thetibia, and an opposite end region adapted for protruding from the kneejoint and coupling with a guide jig for guiding cutting of the or eachone of the tibia and the femur in the resection of the bone, wherein thespacers have a different thickness to one another for providingdifferent spacings of the femur from the tibia.
 81. A set of spacersaccording to claim 80 wherein the leading end region of each said spaceris adapted for retaining the spacer in the knee joint, respectively. 82.A set of spacers according to claim 80 wherein the leading end region ofeach said spacer is adapted for receiving the medial or lateral condyleof the femur and thereby retaining the spacer in the knee joint,respectively.
 83. A set of spacers according to claim 80 wherein theleading end region of each said spacer has an upperside and an oppositeunderside, and a protuberance for being seated on an articulatingsurface of the tibia is defined on the underside of each for spacing thefemur from the tibia.